1. Field of the Invention
The present invention relates to photoresist cross-linker monomers comprising double bonds, photoresist polymers derived from the same and photoresist compositions comprising such polymer. In particular, the present invention relates to acid labile photoresist cross-linker monomers, polymers derived from the same, and photoresist compositions comprising such polymer. The photoresist compositions of the present invention are suitable for photolithography processes employing KrF, ArF, EUV, VUV and similar light sources.
2. Description of the Background Art
Recently, chemical amplification-type DUV photoresists have been investigated to increase sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and a matrix resin polymer (i.e., photoresist polymer) comprising an acid labile group.
In a photolithography process, an exposure of photoresist to light of a particular wavelength generates an acid from the photoacid generator that is present in the photoresist. This generated acid causes the main chain or the branched chain of the resin to decompose or become cross-linked. In addition, the acid removes the acid labile group which is present in the polymer and changes the polarity of the photoresist in the exposed region. This polarity change creates a solubility difference in a developing solution between the exposed portion and the unexposed portion, thereby allowing a pattern formation. The resolution of the pattern that is formed depends on the wavelength of the lightxe2x80x94i.e., in general, a shorter wavelength allows formation of more minute patterns.
In general, a useful photoresist (hereinafter, abbreviated as xe2x80x9cPRxe2x80x9d) has a variety of desired characteristics, such as excellent etching resistance, heat resistance and adhesiveness. In addition, a photoresist should be easily developable in a commercially readily available developing solution, such as 2.38 wt % or 2.6 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a photoresist polymer that satisfies all of these characteristics.
A resin (i.e., photoresist polymer) like novolac resin having high transparency and high etching resistance at 193 nm of wavelength has been investigated. In addition, researchers at the Bell Research Center have investigated improving the etching resistance by increasing the amount of alicyclic units in the polymer backbone of the resin. Furthermore, Fujitsu and Sipri have studied the effect of adding methacrylate and/or acrylate monomers to improve the etching resistance. Unfortunately, the resulting polymers do not have satisfactory etching resistance. Moreover, the cost of producing polymers having increased alicyclic units in the polymer backbone is significantly higher. Furthermore, many photoresist polymers generally have low adhesiveness; therefore, the dense L/S pattern below 150 nm may not form properly.
Therefore, there is a need for a photoresist monomer which provides a polymer having the above described characteristics.
The present inventors have found that the contrast ratio between the exposed region and the unexposed region of a photoresist film can be enhanced by adding a cross-linker monomer having, preferably, two double bonds to the PR polymer. Moreover, it has been found that the addition of cross-linker monomer as a comonomer also improves a pattern profile.
Accordingly, an object of the present invention is to provide a photoresist cross-linker monomer which comprises a double bond, preferably two double bonds. In particular, a cross-linker monomer which comprises an acid labile group.
Another objective of the present invention is to provide a photoresist polymer derived from such photoresist cross-linker monomer. Preferably, the polymer has an excellent etching resistance, reproducibility, durability, adhesiveness and resolution.
Still another objective of the present is to provide a photoresist composition comprising such photoresist polymer.